Technical Field
This invention relates to industrial process stream compositional analysis, and more particularly to an online system for process stream compositional analysis using a headspace column to separate materials of interest from the process stream for analysis.
Background Information
The operations of process plants have been leveraged by the availability of analytical methods, for example, through the use of laboratory measurements or online analyzers. These types of results are valued by plant operations because they are typically regarded as reliable. For example, with respect to hydrocarbon and/or refining operations, primary analytical test methods provide a critical basis for custody transfer of products whose properties have been ascertained in accordance with industry standard test methods such as those developed and promulgated by ASTM International.
Notwithstanding the importance of these primary test methods, they do suffer from certain inadequacies. For example, laboratory measurements typically may be available only once or several times per day. Furthermore, several hours can elapse between the obtaining of a discrete sample and the reporting of results from tests performed on it, severely limiting the possibility to control the process on the basis of those results. Additionally, sample stability, sample contamination, issues of representative sampling, and uncertainty associated with the execution of test procedures may result in erroneous ample values being returned.
Improving the availability, integrity, and reproducibility of test data has in many cases motivated the on-line deployment of measurements. However, depending upon the type of measurement and analysis being performed, the measurement of some liquids, such as hydrocarbon streams, wastewater, and other multi-component process streams, using conventional photometric or spectrometric devices, has been problematic. These liquids, for example, may be too optically dense for the analyzer to get adequate light through the sample. They may also coat the lenses of the analyzer, which tends to decrease analyzer accuracy and increase maintenance time. These liquids may also have unknown irregular background absorption in the spectral region of the particular materials of interest, to further decrease accuracy of readings. Still further, these liquids may contain particulates which block light across the analytical spectrum to create artificially high concentration readings. Liquids may also include air bubbles, which refract the light and scatter it creating artificially high concentration readings. Non-volatile components may also absorb in the spectral region being analyzed, which may be particularly problematic in wastewater analysis.
Even small deviations in measurement accuracy can significantly impact the economies of production for large scale processes similar to those process units found in petroleum refineries and petrochemical plants. There remains a need in the art for improved methods of measuring properties of industrial process streams, such as hydrocarbon streams and other dirty or multi-component streams, preferably on-line in substantially real-time. Furthermore, there remains a need in the art for improved methods of measuring properties of hydrocarbon streams with a high degree of accuracy.